Multiturn potentiometer



April 3, 1962 G. J. MUCHER 3,028,571

MULTITURN POTENTIOMETER Filed Sept. 28, 1960 2 Sheets-Sheet l INVENTOR.

GEORGE J. MU CHER April 1952 G. J. MUCHER 3,028,571

MULTITURN POTENTIOMETER Filed Sept. 28, 1960 2 Sheets-Sheet 2 FIG. 3

l7' l8' l9 F I G. 4

INVENTOR.

GEORGE J. MUCHER United States Patent'Q 3,028,571 MULTITURNPOTENTIOMETER George J. Mucher, Rochester, N.H., assignor to Clarostatlgflfglk Co., Inc, Dover, N.H., a corporation of New Filed Sept. 28,1960, Ser. No. 59,080 Claims. or. 338-143 which moves along thelongitudinal axis of the helix to traverse the various turns thereof inorder to alter the value of the resistance. -The most common methodofmoving the contact arm 'is through use of a rotatable shaftmechanically connected with the contact arm so that rotation of theshaft will effect longitudinal movement of the contact arm. Such anassembly is utilized in equipment wherein high accuracies are sought andthe movement of the contact arm must be accomplished in such a mannerthat little or no electrical error results from the mechanicalconstruction of the device. The rotation of the shaft in assemblies ofthis type is usually accomplished by a servo motor and because of theaccuracies involved it is theoretically desirable to have the extreme ofrotation of the servo motor coincident with the extreme movement of thecontact arm'in both directions. This, of course, is impossible in apractical physical embodiment and one of the main sources of difficultyin the utilization of multiturn potentiometers results from therequirement that if the movement of the shaft and the movement of thecontact arm are not precisely synchronized, the potentiometer is inserious danger of being damaged. To this end various methods have beenused and constructions made to effect a stopping of they contact arm atits extreme position without damaging the assembly even if the shaft isfurther rotated.

The invention herein disclosed has as its principal object thefurnishing of a new multiturn potentiometer of such construction that itcan resist a high degree of turning torque applied to its shaft withoutdamaging the structure even though the contact arm has reached anextreme position.

Another object of this invention is to provide a multiturn potentiometerof rugged construction which suffers vary little backlash and which willnot alter its electrical characteristics because of dirt forming in thetrack in which the contact carrier moves.

A further object of this invention is to provide a multiturnpotentiometer whose movable parts are light in mass, one thatrequireslow torque to move the contact arm, and one that exhibits superiorvibration characteristics.

The invention disclosed herein is described in. terms of a potentiometerby way of example only and it should be understood that the inventiveconcept set forth herein can be applied by one reasonably skilled in theart to other variable parameter components whose value is altered bymoving a contact arm by rotation of a shaft.

A multiturn potentiometer embodying the invention and the manner ofusing the same is described herein with references to the drawings inwhich:

FIG. 1 is an exploded top perspective view of a multiturn potentiometerconstructed in accordance with the teachings of this invention withportions thereof broken away to disclose detailed views of portionsthereof;

FIG. 2 is a segmentary view of a portion of the casing .and winding ofthe potentiometer shown in FIG. 1 as "ice viewed in the direction of thearrow designated with the numeral 2;

FIG. 3 is a partially sectional view taken along the line 3-3 in thedirection of the arrows as indicated in PEG. 1. showing in cross-sectionthe contact driver, contact carrier, and contact arm utilized in thepotentiometer; and

FIG. 4- is a circuit diagram of one possible winding circuitarrangement. I

In FIG. 1 a molded cylindrical casing 10 is shown having a resistanceWire in the form of a helix 11 embedded in the internal surface thereof.The axis of the helix and the axis of the casing are identical. As seenalso in FIG. 2, casing 10 is formed with a helical groove 12 on itsinternal surface so that each turn of resistance wire 11 is separatedfrom adjacent turns by a portion of helical terial can be used for thispurpose. In its preferred form, the external surface of casing 10 isformed with longitudinal slots 13 and through openings 14 in order toaid in assembling certain portions of the device and in order to aid inplacing external casing 15 over casing 10 when the assembly has beencompleted.

External casing 15 is shown in FIG. 1 and in the final assembly thecasing 10 lies within casing 15 and concentric therewith. Openings 14are used to aid in the assembly and to allow leads to be brought fromwithin casing .10 to posts 16, 17, 18 and 19 of terminal block 20 whichis rigidly fastened to the external surface of casing 15. Openings21 incasing 10 and 22 in casing 15 are utilized to maintain the two casingsrigidly together in the final assembly steps. I

One end of casing 15 is closed and a bearing member 23 is embedded inthe internal surface thereof and designed to receive correspondingbearing member 23 which is fashioned at one end of shaft 24 which is theaxis of the driver member indicated generally by the numeral 25 in thefigures. As shown in the figures, the combination of bearing members 23and 23 form a sleeve bearing supporting one end of shaft 24 which ispreferably steel but which could be formed from any suitable material.Although a sleeve bearing assembly is illustrated in the figures, othertypes of bearings can be utilized.

Circular cover 26 is formed with a portion 27 of external diameter sothat it can be received within casing or housing 15 and maintainedtherein by utilization of openings 21, 22and 23. The cover 26 is formedalso from any suitablematerial which is a non-conducting material. 'Inthe preferred form, control housing 15 and cover 26 are molded fromdiallyl phthalate. The cover or liner 10 as set forth above is alsomolded from a non-conducting material. In its preferred form thematerial of which liner 10 is molded is epoxy resin, however, anysuitable material can be used for this purpose.

Body 29 which is-originally attached to shaft 24 contains longitudinalslot 33 extending throughout its length. Longitudinal slot 33 is formedto receive metallic U- channel 3 which in turn forms the track forsliding stop 35. Channel 34 is U-shaped in cross-section forming asubstantially rectangular track in which sliding stop 35 is maintainedagainst rotational movement but free to move longitudinally.

Light weight disk 36 with a section removed from the central portionthereof corresponding generally to the outline of driver member 25 sothat it can receive the same therein, is utilized as a contact carrier.As seen best in FIG. 3 contact carrier 36 is formed to receive thecross-sectional configuration of driver body 29 and to receive radialprojecting portion'iitl thereof within cutout section 37 of carriermember 36. Carrier member 36 is disk-like and has a depth substantiallyequal to the width of helically grooved channel 12 of the liner Carriermember 36 is formed of a light weight material, preferably a plastic,which is non-conducting. An edge thereof at section 36 is receivedwithin slot 35' of moving stop 35. The moving stop is preferablymetallic and the slot 35 formed therein is preferably of sufiicientwidth that section 36' of the carrier member 36 is maintained thereinrelatively snugly. Resilient contact arm 38 is fastened at one end 39 bymeans of bracket 40 and eyelets {i-l to contact carrier 36 andelectrical lead 42 is electrically in contact with contact member 38.

Contact 38 is designed to engage coil 11 when sector 3'6 of contactcarrier 36 is engaged in slot 35' of moving stop 35 and groove 12 ofliner it). Further, contact 33 is positioned on contact carrier 36 sothat the resiliency of arm 38 will yieldingly urge sector 36 Withingroove 12. In order to accomplish this, the point whereat contact 38will engage resistance wirelll is displaced from sector 36? which is tobe urged'thereby'within groove 12.

With such configuration when the driver member 25 i isdisposed with itsends supported in the appropriate bearings, rotation of shaft 24 willresult in the transmission of a rotational force to contact carrier 36through the radially projecting portion 30 of driver 25. This force ofthe disk in the groove in the proper place giving maxi:

mum drive force. The helical groove in which the .contact carrier 36travels is displaced from the coil 11 itself and as a result theformation of dust or dirt of any kind within the groove 12 cannot affectthe electrical characteristics of the device. Additionally, theconcentricity of the major components of the device results in a highly.

accurate assembly.

Thus, among others, the several objects in the invention as specificallyaforenoted, are achieved. Obviously, numerous changes in constructionand rearrangement of parts might be resorted to without departing fromthe spirit of the invention as defined by the claims.

i claim:

1. A multi-turn potentiometer including in combination a cylindricalhollow casing, a helical groove formed on the inner surface of saidcasing, a resistance wire consisting of a plurality of continuous turnsin the form of a helix disposed in the cylindrical plane of said casingwith turns thereof separated by portions of said helical groove,

a driver member rotatably supported within said casing with its axis ofrotation concentric with the axis of said groove and said wire, alongitudinal slot formed in said driver member, a contact carrier, aportion of said contact carrier having the Width of said groove anddisposed therein, a second portion of said contact carrier disposedwithin said slot, means preventing relative rotational will tend to turncontact carrier 36 and move it with groove 12 serving as a tracktherefor so that contact 38 will traverse wire 11 and such traverse canbe accomplished throughout the length of wire 11.

Fixed stops 43 and 4-4 are provided at either end of channel 34 in thecompleted assembly. These stops are preferably metallic and havesurfaces facing channel 34 so that at either of the extreme positions ofcontact carrier 36 movable stop member 35 will abut stop 43 or 44 toprevent further movement of the contact carrier 36 longitudinally. Stop43 is rigidly fastened by any suitable means to the bottom of housing 15in the general vicinity of bearing 23. Stop 44 is rigidly fastened tocover 26 by'any suitable manner in the vicinity of bearing member 28.

Electrically the circuit of the potentiometer shown and described hereinis diagrammatically illustrated'in FIG. 4. In FIG. 4 the various pointsof interest are given numbers corresponding to the numbers given theposts. on terminal board 20 in FIG. '1. In FIG. 4, however, in order toavoid error, the corresponding numbers are set forth as prime numbersand as tap points on resistance 11' which is a diagrammaticindication ofthe resistance of wire 11. Physically, post 16 is electrically connectedto collector arm 45 shown in FIG. l which is designed to engagecollector 46 which is electrically connected with .arm 38. For thispurpose wire 42 is utilized and cutout portion 4'7 of body 29 Post 17 isconnected electrically to one end of wire 11 and post19 is connected tothe remaining end. Post 18 is an optional terminal which can be utilizedif desired.

With such a device many advantages result. The device is low in backlashand there is very little relative rotational motion between the variousparts. The metal inmovement of said contact carrier and said drivermember, a contact arm rigidly supported by said contact carrier and inengagement with one turn of said cell, and conducting means forming anelectrical circuit with said contact arm and said coil.

.2. A multiturn potentiometer in accordance with claim 1 in which thecontact carrier is a lightweight electrically non-conductive discsection and the contact arm is a resilient electrical conductor rigidlyfastened at one end to a surface of the contact carrier so that itengages the coil adjacent the portion of the helical groove in which thecontact carrier is disposed.

3. A multiturn potentiometer in accordance with claim 1 in which thecasing is formed with one surface at each end against which the contactcarrier can abut upon reaching the extremity of travel in thatdirection.

7 4. A multiturn potentiometer in accordance with claim 2 in which theportion of the contact carrier within the helical groove is displacedfrom the contact arm whereby it is yieldingly urged thereby withinsaidhelical groove.

5-. A 'multiturn potentiometer in accordance with claim 4 in which thecontact carrier is formed with a radial .slot and the driver member isformed with a radialpro- .jection disposed within said radial slot insubstantiallya glove fit by which turning moments applied to the drivermember can be imparted to the contact carrier.

6. A multiturn potentiometer including in combination a cylindricalhollow casing, a helical groove formed on the inner surface of saidcasing, a resistance wire con tact carrier having a portion within saidrecess and a portion in said helical groove, means preventing relativerotational movement of said contact carrier and said driver member, acontact arm rigidly supported by said contact carrier and in engagementwith said coil, and conducting means forming an electrical circuit withsaid contact arm; and said coil. I, V V

7. A multiturn potentiometer in accordance with claim 6 in which thecasing is formed with one surface at each end against which the slidingstop can abut upon reaching the extremity of travel in that direction.

8. In a mnltiturn potentiometer a cylindrical hollow casing, aresistance wire consisting of a plurality of continuous turns in theform of a helix concentric with said casing, a helical groove formed insaid casing throughout its efiective length, a driver member rotatablysupported within said casing and said wire with its axis of rotationconcentric with the axis of said casing, a contact member mounted onsaid driver member so that it is longitudinally movable relative theretoand maintained against rotational movement relative thereto and aportion of said contact member disposed within said helical groovewhereby rotation of said driver member can cause said contact member tomove longitudinally and traverse the turns of said resistance wire, saidcontact member being formed with an irregular slot therein and saiddriver member is formed to be received in said slot, and a longitudinalgroove is formed in said driver member and said contact member is formedwith a section thereof to be movably disposed in said longitudinalgroove. I

9. In a multiturn potentiometer, a cylindrical hollow casing, aresistance wire consisting of a plurality of continuous turns in theform of a helix concentric with said casing, a helical groove formed insaid casing throughout its efiective length and separating each turn ofsaid resistance wire from adjacent turns, a driver member rotatablysupported with its axis of rotation concentric with the axis of saidcasing, a contact member mounted on said driver member so that it islongitudinally movable relative thereto and maintained againstrotational movement relative thereto, a longitudinal groove formed insaid driver member, a section of said contact member movably disposed insaid longitudinal groove, and a portion of said contact member disposedwithin said helical groove whereby rotation of said driver member cancause said contact member to move longitudinally and traverse the turnsof said resistance wire.

10. In a multiturn potentiometer, a cylindrical hollow casing, aresistance wire consisting of a plurality of continuous turns in theform of a helix concentric with said casing, a helical groove formed insaid casing throughout its effective length and separating each turn ofsaid resistauce wire from adjacent turns, a driver member rotatablysupported with its axis of rotation concentric with the axis of saidcasing, a contact member, an irregular slot formed in said contactmember, said driver memher being formed to be received in said irregularslot so that said contact member is longitudinally movable relativethereto and maintained against rotational movement relative thereto anda portion of said contact member disposed within said helical groovewhereby rotation of said driver member can cause said contact member tomove longitudinally and traverse the turns of said resistance wire.

References Cited in the file of this patent 2,813,956 Sorber Nov. 19,1957 Beckman Nov. 30, 1948

